Stretch films are widely used in a variety of bundling and packaging applications. For example, stretch films have become a common method of securing bulky loads such as boxes, merchandise, produce, equipment, parts, and other similar items on pallets. Such films are typically made from various polyethylene resins and are single or multilayer products. An additive known as a cling agent is frequently used to ensure that adjacent layers of film will cling to each other.
Typical stretch films are comprised of multiple discrete layers that allow for the overall performance of the film to be modified by the use of differentiated resins in any of the internal or external layers of the structure. The majority of high-performance, thin gauge machine stretch films typically incorporate high levels (e.g., greater than 50% by weight) metallocene linear low density polyethylene resins (m-LLDPE) in the structure. The m-LLDPE resins offer enhanced stretch and puncture performance over Ziegler-Natta (ZN) LLDPE resins, thereby allowing the production of thinner, more durable films.
Although films incorporating a high level of m-LLDPE resin benefit from elongation and puncture improvements versus conventional ZN LLDPE resins, the m-LLDPE products are still susceptible to catastrophic failure when penetrated. Catastrophic failure is defined as a complete separation of the film under normal stretch wrapping conditions due to a minimal penetration. This accelerated failure mechanism is generally not observed in films incorporating a high level of ZN LLDPE resin, but can be a concern with films having a high level of m-LLDPE resin.
Catastrophic failure typically occurs at a speed that prevents the film from establishing and maintaining a film web between the pallet wrapper and the pallet being wrapped.
There is, therefore, a long-standing yet unmet need for stretch films which incorporate a high level of m-LLDPE resin, while avoiding catastrophic failure. There is a further unmet need for methods of producing such films.